The aim of the project is to measure arterial blood gas tensions (PO2 and PCO2) by a new, non-invasive method in patients with cardio- pulmonary disease. A mass spectrometer will be used to sample the gases diffusing from capillary blood through specially prepared human skin. A sampling chamber will be constructed with a limiting membrane, through which the gas, which diffuses through the skin, will pass directly to the ionization chamber of the mass spectrometer, at a rate of approximately 1 x 10 to the minus 5th power ml/sec. Different skin sites (e.g. ear, forehead and neck) and different means of skin preparation (heating, decornification and chemical vaso-dilation alone or in combination) will be tested, in an attempt to maximize both skin blood flow, and gas diffusion across the skin. Skin temperature and skin electrical resistance measurements will be used to control the adequancy of the skin preparation. Nitrogen tension in the chamber will be measured to determine the adequacy of skin flow at the sampling site. The system of skin sampling will be tested in normal subjects, and in adults and infants with pulmonary diseases, and its validity, accuracy, and applicability determined.